Signaling HRD parameters for bitstream partitions

ABSTRACT

In one example, a device for coding (e.g., encoding or decoding) video data includes a memory configured to store video data, and a video coder configured to code a value for a syntax element that indicates a number of sub-layers of a bitstream for which hypothetical reference decoder (HRD) parameters are coded, wherein the value indicates that the number of sub-layers for which HRD parameters are coded is less than a maximum number of sub-layers indicated by a video parameter set (VPS) of the bitstream, code HRD parameters for the number of sub-layers as indicated by the value for the syntax element, and process the bitstream using the HRD parameters.

This application claims the benefit of U.S. Provisional Application No.62/013,965, filed Jun. 18, 2014, which is hereby incorporated byreference in its entirety.

TECHNICAL FIELD

This disclosure relates to video coding.

BACKGROUND

Digital video capabilities can be incorporated into a wide range ofdevices, including digital televisions, digital direct broadcastsystems, wireless broadcast systems, personal digital assistants (PDAs),laptop or desktop computers, tablet computers, e-book readers, digitalcameras, digital recording devices, digital media players, video gamingdevices, video game consoles, cellular or satellite radio telephones,so-called “smart phones,” video teleconferencing devices, videostreaming devices, and the like. Digital video devices implement videocoding techniques, such as those described in the standards defined byMPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced VideoCoding (AVC), the High Efficiency Video Coding (HEVC) standard presentlyunder development, and extensions of such standards. The video devicesmay transmit, receive, encode, decode, and/or store digital videoinformation more efficiently by implementing such video codingtechniques.

Video coding techniques include spatial (intra-picture) predictionand/or temporal (inter-picture) prediction to reduce or removeredundancy inherent in video sequences. For block-based video coding, avideo slice (e.g., a video frame or a portion of a video frame) may bepartitioned into video blocks, which may also be referred to astreeblocks, coding units (CUs) and/or coding nodes. Video blocks in anintra-coded (I) slice of a picture are encoded using spatial predictionwith respect to reference samples in neighboring blocks in the samepicture. Video blocks in an inter-coded (P or B) slice of a picture mayuse spatial prediction with respect to reference samples in neighboringblocks in the same picture or temporal prediction with respect toreference samples in other reference pictures. Pictures may be referredto as frames, and reference pictures may be referred to as referenceframes.

Spatial or temporal prediction results in a predictive block for a blockto be coded. Residual data represents pixel differences between theoriginal block to be coded and the predictive block. An inter-codedblock is encoded according to a motion vector that points to a block ofreference samples forming the predictive block, and the residual dataindicating the difference between the coded block and the predictiveblock. An intra-coded block is encoded according to an intra-coding modeand the residual data. For further compression, the residual data may betransformed from the pixel domain to a transform domain, resulting inresidual transform coefficients, which then may be quantized. Thequantized transform coefficients, initially arranged in atwo-dimensional array, may be scanned in order to produce aone-dimensional vector of transform coefficients, and entropy coding maybe applied to achieve even more compression.

SUMMARY

In general, this disclosure describes techniques for signalinghypothetical reference decoder (HRD) parameters for bitstreampartitions. That is, the techniques of this disclosure may improvesignaling of HRD parameters for bitstream partitions, e.g., inmulti-layer video coding. A video bitstream may include various layersin various dimensions, such as a temporal dimension, a view dimension(e.g., for multi-view video data), a scalability dimension (e.g., forscalable video coding), or the like. Various techniques, which may beused alone or in any combination, are described that may improve HRDparameter signaling for bitstream partitions, any or all of which may beindividually extracted for subsequent decoding by a video decoder.

In one example, a method of coding (e.g., encoding or decoding) videodata includes coding a value for a syntax element that indicates anumber of sub-layers of a bitstream for which hypothetical referencedecoder (HRD) parameters are coded, wherein the value indicates that thenumber of sub-layers for which HRD parameters are coded is less than amaximum number of sub-layers indicated by a video parameter set (VPS) ofthe bitstream, coding HRD parameters for the number of sub-layers asindicated by the value for the syntax element, and processing thebitstream using the HRD parameters.

In another example, a device for coding (e.g., encoding or decoding)video data includes a memory configured to store video data, and a videocoder configured to code a value for a syntax element that indicates anumber of sub-layers of a bitstream for which hypothetical referencedecoder (HRD) parameters are coded, wherein the value indicates that thenumber of sub-layers for which HRD parameters are coded is less than amaximum number of sub-layers indicated by a video parameter set (VPS) ofthe bitstream, code HRD parameters for the number of sub-layers asindicated by the value for the syntax element, and process the bitstreamusing the HRD parameters.

In another example, a device for coding (e.g., encoding or decoding)video data includes means for coding a value for a syntax element thatindicates a number of sub-layers of a bitstream for which hypotheticalreference decoder (HRD) parameters are coded, wherein the valueindicates that the number of sub-layers for which HRD parameters arecoded is less than a maximum number of sub-layers indicated by a videoparameter set (VPS) of the bitstream, means for coding HRD parametersfor the number of sub-layers as indicated by the value for the syntaxelement, and means for processing the bitstream using the HRDparameters.

In another example, a computer-readable storage medium is encoded withinstructions that, when executed, cause one or more processors to code avalue for a syntax element that indicates a number of sub-layers of abitstream for which hypothetical reference decoder (HRD) parameters arecoded, wherein the value indicates that the number of sub-layers forwhich HRD parameters are coded is less than a maximum number ofsub-layers indicated by a video parameter set (VPS) of the bitstream,code HRD parameters for the number of sub-layers as indicated by thevalue for the syntax element, and process the bitstream using the HRDparameters.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system that may utilize techniques for improving hypotheticalreference decoder (HRD) parameter signaling.

FIG. 2 is a block diagram illustrating an example of a video encoderthat may implement techniques for improving hypothetical referencedecoder (HRD) parameter signaling.

FIG. 3 is a block diagram illustrating an example of a video decoderthat may implement techniques for improving hypothetical referencedecoder (HRD) parameter signaling.

FIG. 4 is a flowchart illustrating an example method for encoding videodata according to the techniques of this disclosure.

FIG. 5 is a flowchart illustrating an example method for decoding videodata according to the techniques of this disclosure.

DETAILED DESCRIPTION

In general, this disclosure describes techniques related to coding(e.g., encoding or decoding) hypothetical reference decoder (HRD)parameters. In general, HRD parameters are used to manage timelines aswell as to control sizes of coded picture for a video coding process.For example, a video coder may use the HRD parameters to determine whento extract an encoded picture from a coded picture buffer (CPB), forpurposes of decoding the picture, and/or to determine when to extract,output, and/or remove a decoded picture from a decoded picture buffer(DPB).

A video bitstream may include coded video data that can be used by avariety of different decoding and rendering devices. For instance, avideo decoder may support various video coding standard profiles andlevels, which may implement various decoding tools. Similarly, a videorendering device (e.g., a display) may support various renderingcapabilities (e.g., refresh rate/frame rate, number of views that can beplayed simultaneously, interlaced or progressive scan playback, or thelike). In this manner, a single video bitstream may be usable bymultiple different video decoders and rendering devices.

As one example, a video bitstream may be said to support temporalscalability when various frame rates can be rendered from the videobitstream. For example, the same video bitstream may be used to rendervideo having frame rates of 15 frames per second (FPS), 30 FPS, 60 FPS,120 FPS, and 240 FPS. In general, each of these various playback framerates corresponds to a set of one or more “sub-layers” of the bitstream.Each progressively higher layer includes all frames at that sub-layerand below that sub-layer. Thus, the pictures for the 15 FPS playback mayinclude sub-layer 0 pictures, the pictures for the 30 FPS playback mayinclude sub-layers 0 and sub-layer 1 pictures, the pictures for the 60FPS playback may include pictures of sub-layers 0, 1, and 2, and so on.

In this manner, when a device is configured to perform playback at aframe rate lower than a maximum frame rate supported by a videobitstream, the device may perform sub-bitstream extraction from thebitstream, to extract and decode only the pictures needed for playback.Continuing the example above, if the device were to determine to perform60 FPS playback, the device may extract the pictures of sub-layers 0, 1,and 2, and decode only these pictures (i.e., without decoding picturesof sub-layers 3 and 4).

A video parameter set (VPS) syntax structure may include data indicatinga maximum number of sub-layers that can be included in a bitstream.Thus, HRD parameters may be signaled for each of the maximum number ofsub-layers. However, sub-bitstream extraction (e.g., for purposes oftemporal scalability) may result in an extracted sub-bitstream havingfewer than the maximum number of sub-layers. Rather than signalinginformation for each of the maximum number of sub-layers, thisdisclosure describes techniques for signaling HRD parameters only forthe number of sub-layers that are actually included in a bitstream(which may be less than or equal to the maximum number of sub-layersindicated by the VPS). In this manner, these techniques may achieve abit savings relative to techniques in which HRD parameters are signaledfor each of the maximum number of sub-layers.

Similarly, this disclosure describes techniques for signaling HRDparameters for each sub-layer of each partition of a bitstream. Forexample, the VPS may include a loop of parameters that iterates overeach of the number of possible output layer sets, and for each possibleoutput layer sets, signals HRD parameters for sub-layers included in thecorresponding output layer set.

Furthermore, this disclosure describes techniques for conditionallysignaling video coding layer (VCL) HRD parameters in a bitstreampartition initial arrival time supplemental enhancement information(SEI) message. This may overcome certain potential deficiencies ofexisting techniques in which such parameters may be signaledunnecessarily in certain conditions.

The techniques of this disclosure are generally described with respectto ITU-T H.265, also referred to as High Efficiency Video Coding (HEVC),which is described in “SERIES H: AUDIOVISUAL AND MULTIMEDIA SYSTEMS,Infrastructure of audiovisual services—Coding of moving video,” HighEfficiency Video Coding, ITU-T H.265, April 2013. However, thesetechniques may be applied to other video coding standards as well. Videocoding standards include ITU-T H.261, ISO/IEC MPEG-1 Visual, ITU-T H.262or ISO/IEC MPEG-2 Visual, ITU-T H.263, ISO/IEC MPEG-4 Visual and ITU-TH.264 (also known as ISO/IEC MPEG-4 AVC), including its Scalable VideoCoding (SVC) and Multiview Video Coding (MVC) extensions.

The H.265 standard was recently finalized by the Joint CollaborationTeam on Video Coding (JCT-VC) of ITU-T Video Coding Experts Group (VCEG)and ISO/IEC Motion Picture Experts Group (MPEG). The latest HEVC draftspecification, and referred to as HEVC WD hereinafter, is available fromphenix.it-sudparis.eu/jct/doc_end_user/documents/17_Valencia/wg11/JCTVC-Q1003-v1.zip.The multiview extension to HEVC, namely MV-HEVC, is also being developedby the JCT-3V. A recent Working Draft (WD) of MV-HEVC, referred to asMV-HEVC WD8 hereinafter, is available fromphenix.it-sudparis.eu/jct2/doc_end_user/documents/8_Valencia/wg11/JCT3V-H1002-v5.zip.The scalable extension to HEVC, named SHVC, is also being developed bythe JCT-VC. A recent Working Draft (WD) of SHVC and referred to as SHVCWD6 hereinafter, is available fromphenix.it-sudparis.eu/jct/doc_end_user/documents/17_Valencia/wg11/JCTVC-Q1008-v2.zip.

MV-HEVC WD8 and SHVC WD6 include the specification of a bitstreampartition based HRD operation, called bitstream-partition-specific HRDoperation, wherein layers of a bitstream can be divided into more thanone bitstream partitions, and the HRD may operate based onbitstream-partition-specific HRD parameters.

JCTVC-R0043v5 (available atphenix.int-evey.fr/jct/doc_end_user/documents/18_Sapporo/wg11/JCTVC-R0043-v5.zip)and the AHG10 output text in attachments to Sullivan, “Ad hoc groupreport: Layered coding constraint specifications and capabilityindications (AHG10),” Joint Collaborative Team on Video Coding (JCT-VC)of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11, 18^(th) Meeting:Sapporo, JP, 30 Jun. to 9 Jul. 2014, JCTVC-R0010v2, (hereinafter,“JCTVC-R0010v2”), available atphenix.int-evey.fr/jct/doc_end_user/documents/18_Sapporo/wg11/JCTVC-R0010-v2.zipinclude specifications of a bitstream partition based signalling ofprofile/tier/level and conformance definition. The approach issummarized as follows:

-   -   For each output layer set, one or more partitioning schemes of        layers into partitions are signalled. Each bitstream partition        can contain one or more layers.    -   A set of profile, tier, and level (PTL) is signalled for each        bitstream partition.    -   All level limits and restrictions, except for the three on        picture width, picture height, and sub-DPB size that naturally        layer specific, are specified to be bitstream partition        specific.    -   A decoder's decoding capability is expressed as conforming to a        list of PTL triplets, wherein the number of entries in the list        indicates the number of single-layer decoders used to build the        multi-layer decoder, and each PTL triplet indicates the PTL of        one of the single-layer decoders.    -   A decoder that conforms to a list of PTL triplets is required to        be able to decode any output layer set for which there is at        least one partitioning scheme that satisfies the following        condition: for each bitstream partition of the partitioning        scheme one of the single-layer decoders of the multi-layer        decoder can be exclusively assigned for decoding the bitstream        partition.    -   The bitstream partition based HRD operation in MV-HEVC WD8 and        SHVC WD6 is used with modifications to work better with multiple        partitioning schemes.

In the bitstream partition based HRD operation in MV-HEVC WD8, SHVC WD6,and JCTVC-R0010v2, HRD parameters are signalled for each bitstreampartition. The existing methods for signalling of HRD parameters forbitstream partitions may encounter the following shortcomings:

-   -   1) Each hrd_parameters( ) syntax structure contains information        for vps_max_sub_layer_minus1+1 sub-layers, even the syntax        structure applies to a bitstream has a number of sub-layers that        is less than vps_max_sub_layer_minus1+1. In this case some bits        are purely wasted.    -   2) For each bitstream partition, the HRD parameters for only the        highest sub-layer is signalled, thus the conformance of a        temporal subset of the bitstream partition cannot be defined and        there is no way to consume only a temporal subset of an output        layer set in an interoperable manner.    -   3) In the bitstream partition initial arrival time SEI message,        both of the following two cases that should never occur can        occur:        -   a. When NalHrdBpPresentFlag is 1, the initial arrival delay            for VCL HRD parameters through vcl_initial_arrival_delay[i]            syntax elements are not signalled even if            VclHrdBpPresentFlag is equal to 1. In this case, the VCL HRD            conformance cannot be defined.        -   b. When NalHrdBpPresentFlag is 0 the initial arrival delay            for VCL HRD parameters through vcl_initial_arrival_delay[i]            syntax elements are signalled even if VclHrdBpPresentFlag is            equal to 0. In this case, those signalling are purely            wasting bits.

Thus, as noted above, this disclosure describes various techniques thatmay be used alone or in any combination, and that may overcome any orall of the shortcomings discussed above. A summary of the techniques ofthis disclosure is given below, with a detailed implementation of somemethods provided in later sections. In general, the numbered items belowmay address the numbered shortcomings discussed above:

-   -   1) Each hrd_parameters( ) syntax structure contains information        for the number of sub-layers that is needed, as signalled by a        syntax element, e.g. named num_sub_layer_hrd_minus1[i].    -   2) For each bitstream partition, the HRD parameters for each        sub-layer are signalled. This can be achieved by either adding a        loop with the number entries equal to the number of sub-layers        in the output layer set for the syntax elements indicating the        number of delivery schedules, the index to the list of        hrd_parameters( ) syntax structures, and the index to the list        of delivery schedules in the indicated hrd_parameters( ) syntax        structure, or simply signal only an index to the list of        hrd_parameters( ) syntax structure and use all delivery        schedules in the indicated hrd_parameters( ) syntax structure.    -   3) In the bitstream partition initial arrival time SEI message        syntax is changed such that the initial arrival delay for VCL        HRD parameters are present if and only if VclHrdBpPresentFlag is        equal to 1.

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system 10 that may utilize techniques for improvinghypothetical reference decoder (HRD) parameter signaling. As shown inFIG. 1, system 10 includes a source device 12 that provides encodedvideo data to be decoded at a later time by a destination device 14. Inparticular, source device 12 provides the video data to destinationdevice 14 via a computer-readable medium 16. Source device 12 anddestination device 14 may comprise any of a wide range of devices,including desktop computers, notebook (i.e., laptop) computers, tabletcomputers, set-top boxes, telephone handsets such as so-called “smart”phones, so-called “smart” pads, televisions, cameras, display devices,digital media players, video gaming consoles, video streaming device, orthe like. In some cases, source device 12 and destination device 14 maybe equipped for wireless communication.

Destination device 14 may receive the encoded video data to be decodedvia computer-readable medium 16. Computer-readable medium 16 maycomprise any type of medium or device capable of moving the encodedvideo data from source device 12 to destination device 14. In oneexample, computer-readable medium 16 may comprise a communication mediumto enable source device 12 to transmit encoded video data directly todestination device 14 in real-time. The encoded video data may bemodulated according to a communication standard, such as a wirelesscommunication protocol, and transmitted to destination device 14. Thecommunication medium may comprise any wireless or wired communicationmedium, such as a radio frequency (RF) spectrum or one or more physicaltransmission lines. The communication medium may form part of apacket-based network, such as a local area network, a wide-area network,or a global network such as the Internet. The communication medium mayinclude routers, switches, base stations, or any other equipment thatmay be useful to facilitate communication from source device 12 todestination device 14.

In some examples, encoded data may be output from output interface 22 toa storage device. Similarly, encoded data may be accessed from thestorage device by input interface. The storage device may include any ofa variety of distributed or locally accessed data storage media such asa hard drive, Blu-ray discs, DVDs, CD-ROMs, flash memory, volatile ornon-volatile memory, or any other suitable digital storage media forstoring encoded video data. In a further example, the storage device maycorrespond to a file server or another intermediate storage device thatmay store the encoded video generated by source device 12. Destinationdevice 14 may access stored video data from the storage device viastreaming or download. The file server may be any type of server capableof storing encoded video data and transmitting that encoded video datato the destination device 14. Example file servers include a web server(e.g., for a website), an FTP server, network attached storage (NAS)devices, or a local disk drive. Destination device 14 may access theencoded video data through any standard data connection, including anInternet connection. This may include a wireless channel (e.g., a Wi-Ficonnection), a wired connection (e.g., DSL, cable modem, etc.), or acombination of both that is suitable for accessing encoded video datastored on a file server. The transmission of encoded video data from thestorage device may be a streaming transmission, a download transmission,or a combination thereof.

The techniques of this disclosure are not necessarily limited towireless applications or settings. The techniques may be applied tovideo coding in support of any of a variety of multimedia applications,such as over-the-air television broadcasts, cable televisiontransmissions, satellite television transmissions, Internet streamingvideo transmissions, such as dynamic adaptive streaming over HTTP(DASH), digital video that is encoded onto a data storage medium,decoding of digital video stored on a data storage medium, or otherapplications. In some examples, system 10 may be configured to supportone-way or two-way video transmission to support applications such asvideo streaming, video playback, video broadcasting, and/or videotelephony.

In the example of FIG. 1, source device 12 includes video source 18,video encoder 20, and output interface 22. Destination device 14includes input interface 28, video decoder 30, and display device 32. Inaccordance with this disclosure, video encoder 20 of source device 12may be configured to apply the techniques for improving hypotheticalreference decoder (HRD) parameter signaling. In other examples, a sourcedevice and a destination device may include other components orarrangements. For example, source device 12 may receive video data froman external video source 18, such as an external camera. Likewise,destination device 14 may interface with an external display device,rather than including an integrated display device.

As noted above, source device 12 includes output interface 22 anddestination device 14 includes input interface 28. In some examples,output interface 22 represents a transmitter and input interface 28represents a receiver. In other examples, output interface 22 and inputinterface 28 represent examples of transceivers (that is, interfacescapable of both transmitting and receiving data signals wirelessly). Thetransceivers may be configured to send and receive video data inwireless signals. For example, output interface 22, when implemented asa transceiver, may send a data signal (e.g., computer-readable medium16) including encoded video data, while input interface 28, whenimplemented as a transceiver, may receive a data signal (e.g.,computer-readable medium 16) including encoded video data. As discussedabove, video encoder 20 may provide the encoded video data to outputinterface 22, while input interface 28 may provide encoded video data tovideo decoder 30. Furthermore, the transceiver may include both atransmitter and a receiver, and therefore, any sending actions describedwith respect to the transceiver may also be performed by a transmitter,while receiving actions described with respect to the transceiver mayalso be performed by a receiver.

The illustrated system 10 of FIG. 1 is merely one example. Techniquesfor improving hypothetical reference decoder (HRD) parameter signalingmay be performed by any digital video encoding and/or decoding device.Although generally the techniques of this disclosure are performed by avideo encoding device, the techniques may also be performed by a videoencoder/decoder, typically referred to as a “CODEC.” Moreover, thetechniques of this disclosure may also be performed by a videopreprocessor. Source device 12 and destination device 14 are merelyexamples of such coding devices in which source device 12 generatescoded video data for transmission to destination device 14. In someexamples, devices 12, 14 may operate in a substantially symmetricalmanner such that each of devices 12, 14 include video encoding anddecoding components. Hence, system 10 may support one-way or two-wayvideo transmission between video devices 12, 14, e.g., for videostreaming, video playback, video broadcasting, or video telephony.

Video source 18 of source device 12 may include a video capture device,such as a video camera, a video archive containing previously capturedvideo, and/or a video feed interface to receive video from a videocontent provider. As a further alternative, video source 18 may generatecomputer graphics-based data as the source video, or a combination oflive video, archived video, and computer-generated video. In some cases,if video source 18 is a video camera, source device 12 and destinationdevice 14 may form so-called camera phones or video phones. As mentionedabove, however, the techniques described in this disclosure may beapplicable to video coding in general, and may be applied to wirelessand/or wired applications. In each case, the captured, pre-captured, orcomputer-generated video may be encoded by video encoder 20. The encodedvideo information may then be output by output interface 22 onto acomputer-readable medium 16.

Computer-readable medium 16 may include transient media, such as awireless broadcast or wired network transmission, or storage media (thatis, non-transitory storage media), such as a hard disk, flash drive,compact disc, digital video disc, Blu-ray disc, or othercomputer-readable media. In some examples, a network server (not shown)may receive encoded video data from source device 12 and provide theencoded video data to destination device 14, e.g., via networktransmission. Similarly, a computing device of a medium productionfacility, such as a disc stamping facility, may receive encoded videodata from source device 12 and produce a disc containing the encodedvideo data. Therefore, computer-readable medium 16 may be understood toinclude one or more computer-readable media of various forms, in variousexamples.

Input interface 28 of destination device 14 receives information fromcomputer-readable medium 16. The information of computer-readable medium16 may include syntax information defined by video encoder 20, which isalso used by video decoder 30, that includes syntax elements thatdescribe characteristics and/or processing of blocks and other codedunits, e.g., GOPs. Display device 32 displays the decoded video data toa user, and may comprise any of a variety of display devices such as acathode ray tube (CRT), a liquid crystal display (LCD), a plasmadisplay, an organic light emitting diode (OLED) display, or another typeof display device.

Video encoder 20 and video decoder 30 may operate according to a videocoding standard, such as the High Efficiency Video Coding (HEVC)standard, also referred to as ITU-T H.265. Alternatively, video encoder20 and video decoder 30 may operate according to other proprietary orindustry standards, such as the ITU-T H.264 standard, alternativelyreferred to as MPEG-4, Part 10, Advanced Video Coding (AVC), orextensions of such standards. The techniques of this disclosure,however, are not limited to any particular coding standard. Otherexamples of video coding standards include MPEG-2 and ITU-T H.263.Although not shown in FIG. 1, in some aspects, video encoder 20 andvideo decoder 30 may each be integrated with an audio encoder anddecoder, and may include appropriate MUX-DEMUX units, or other hardwareand software, to handle encoding of both audio and video in a commondata stream or separate data streams. If applicable, MUX-DEMUX units mayconform to the ITU H.223 multiplexer protocol, or other protocols suchas the user datagram protocol (UDP).

Video encoder 20 and video decoder 30 each may be implemented as any ofa variety of suitable encoder circuitry, such as one or moremicroprocessors, digital signal processors (DSPs), application specificintegrated circuits (ASICs), field programmable gate arrays (FPGAs),discrete logic, software, hardware, firmware or any combinationsthereof. When the techniques are implemented partially in software, adevice may store instructions for the software in a suitable,non-transitory computer-readable medium and execute the instructions inhardware using one or more processors to perform the techniques of thisdisclosure. Each of video encoder 20 and video decoder 30 may beincluded in one or more encoders or decoders, either of which may beintegrated as part of a combined encoder/decoder (CODEC) in a respectivedevice.

In general, a video frame or picture may be divided into a sequence oftreeblocks, which are also known as largest coding units (LCUs), thatmay include both luma and chroma samples. Syntax data within a bitstreammay define a size for the LCU, which is a largest coding unit in termsof the number of pixels. A slice includes a number of consecutivetreeblocks in coding order. A video frame or picture may be partitionedinto one or more slices. Each treeblock may be split into coding units(CUs) according to a quadtree data structure. In general, a quadtreedata structure includes one node per CU, with a root node correspondingto the treeblock. If a CU is split into four sub-CUs, the nodecorresponding to the CU includes four leaf nodes, each of whichcorresponds to one of the sub-CUs.

Each node of the quadtree data structure may provide syntax data for thecorresponding CU. For example, a node in the quadtree may include asplit flag, indicating whether the CU corresponding to the node is splitinto sub-CUs. Syntax elements for a CU may be defined recursively, andmay depend on whether the CU is split into sub-CUs. If a CU is not splitfurther, it is referred as a leaf-CU. In this disclosure, four sub-CUsof a leaf-CU are also referred to as leaf-CUs even if there is noexplicit splitting of the original leaf-CU. For example, if a CU at16×16 size is not split further, the four 8×8 sub-CUs are also referredto as leaf-CUs although the 16×16 CU was never split.

A CU has a similar purpose as a macroblock of the H.264 standard, exceptthat a CU does not have a size distinction. For example, a treeblock maybe split into four child nodes (also referred to as sub-CUs), and eachchild node may in turn be a parent node and be split into another fourchild nodes. A final, unsplit child node, referred to as a leaf node ofthe quadtree, comprises a coding node, also referred to as a leaf-CU.Syntax data associated with a coded bitstream may define a maximumnumber of times a treeblock may be split, referred to as a maximum CUdepth, and may also define a minimum size of the coding nodes.Accordingly, a bitstream may also define a smallest coding unit (SCU).This disclosure uses the term “block” to refer to any of a CU,prediction unit (PU), or transform unit (TU), in the context of HEVC, orsimilar data structures in the context of other standards (e.g.,macroblocks and sub-blocks thereof in H.264/AVC).

A CU includes a coding node and prediction units (PUs) and transformunits (TUs) associated with the coding node. A size of the CUcorresponds to a size of the coding node and is generally square inshape. The size of the CU may range from 8×8 pixels up to the size ofthe treeblock with a maximum size, e.g., 64×64 pixels or greater. EachCU may contain one or more PUs and one or more TUs. Syntax dataassociated with a CU may describe, for example, partitioning of the CUinto one or more PUs. Partitioning modes may differ between whether theCU is skip or direct mode encoded, intra-prediction mode encoded, orinter-prediction mode encoded. PUs may be partitioned to be non-squarein shape. Syntax data associated with a CU may also describe, forexample, partitioning of the CU into one or more TUs according to aquadtree. A TU can be square or non-square (e.g., rectangular) in shape.

The HEVC standard allows for transformations according to TUs, which maybe different for different CUs. The TUs are typically sized based on thesize of PUs within a given CU defined for a partitioned LCU, althoughthis may not always be the case. The TUs are typically the same size orsmaller than the PUs. In some examples, residual samples correspondingto a CU may be subdivided into smaller units using a quadtree structureknown as “residual quad tree” (RQT). The leaf nodes of the RQT may bereferred to as transform units (TUs). Pixel difference values associatedwith the TUs may be transformed to produce transform coefficients, whichmay be quantized.

A leaf-CU may include one or more PUs. In general, a PU represents aspatial area corresponding to all or a portion of the corresponding CU,and may include data for retrieving and/or generating a reference samplefor the PU. Moreover, a PU includes data related to prediction. Forexample, when the PU is intra-mode encoded, data for the PU may beincluded in a residual quadtree (RQT), which may include data describingan intra-prediction mode for a TU corresponding to the PU. The RQT mayalso be referred to as a transform tree. In some examples, theintra-prediction mode may be signaled in the leaf-CU syntax, instead ofthe RQT. As another example, when the PU is inter-mode encoded, the PUmay include data defining motion information, such as one or more motionvectors, for the PU. The data defining the motion vector for a PU maydescribe, for example, a horizontal component of the motion vector, avertical component of the motion vector, a resolution for the motionvector (e.g., one-quarter pixel precision or one-eighth pixelprecision), a reference picture to which the motion vector points,and/or a reference picture list (e.g., List 0, List 1, or List C) forthe motion vector.

A leaf-CU having one or more PUs may also include one or more TUs. Thetransform units may be specified using an RQT (also referred to as a TUquadtree structure), as discussed above. For example, a split flag mayindicate whether a leaf-CU is split into four transform units. Then,each transform unit may be split further into further sub-TUs. When a TUis not split further, it may be referred to as a leaf-TU. Generally, forintra coding, all the leaf-TUs belonging to a leaf-CU share the sameintra prediction mode. That is, the same intra-prediction mode isgenerally applied to calculate predicted values for all TUs of aleaf-CU. For intra coding, a video encoder may calculate a residualvalue for each leaf-TU using the intra prediction mode, as a differencebetween the portion of the CU corresponding to the TU and the originalblock. A TU is not necessarily limited to the size of a PU. Thus, TUsmay be larger or smaller than a PU. For intra coding, a PU may becollocated with a corresponding leaf-TU for the same CU. In someexamples, the maximum size of a leaf-TU may correspond to the size ofthe corresponding leaf-CU.

Moreover, TUs of leaf-CUs may also be associated with respectivequadtree data structures, referred to as residual quadtrees (RQTs) ortransform trees as noted above. That is, a leaf-CU may include aquadtree indicating how the leaf-CU is partitioned into TUs. The rootnode of a TU quadtree generally corresponds to a leaf-CU, while the rootnode of a CU quadtree generally corresponds to a treeblock (or LCU). TUsof the RQT that are not split are referred to as leaf-TUs. In general,this disclosure uses the terms CU and TU to refer to leaf-CU andleaf-TU, respectively, unless noted otherwise.

A video sequence typically includes a series of video frames orpictures. A group of pictures (GOP) generally comprises a series of oneor more of the video pictures. A GOP may include syntax data in a headerof the GOP, a header of one or more of the pictures, or elsewhere, thatdescribes a number of pictures included in the GOP. Each slice of apicture may include slice syntax data that describes an encoding modefor the respective slice. Video encoder 20 typically operates on videoblocks within individual video slices in order to encode the video data.A video block may correspond to a coding node within a CU. The videoblocks may have fixed or varying sizes, and may differ in size accordingto a specified coding standard.

As an example, prediction may be performed for PUs of various sizes.Assuming that the size of a particular CU is 2N×2N, intra-prediction maybe performed on PU sizes of 2N×2N or N×N, and inter-prediction may beperformed on symmetric PU sizes of 2N×2N, 2N×N, N×2N, or N×N. Asymmetricpartitioning for inter-prediction may also be performed for PU sizes of2N×nU, 2N×nD, nL×2N, and nR×2N. In asymmetric partitioning, onedirection of a CU is not partitioned, while the other direction ispartitioned into 25% and 75%. The portion of the CU corresponding to the25% partition is indicated by an “n” followed by an indication of “Up”,“Down,” “Left,” or “Right.” Thus, for example, “2N×nU” refers to a 2N×2NCU that is partitioned horizontally with a 2N×0.5N PU on top and a2N×1.5N PU on bottom.

In this disclosure, “N×N” and “N by N” may be used interchangeably torefer to the pixel dimensions of a video block in terms of vertical andhorizontal dimensions, e.g., 16×16 pixels or 16 by 16 pixels. Ingeneral, a 16×16 block has 16 pixels in a vertical direction (y=16) and16 pixels in a horizontal direction (x=16). Likewise, an N×N blockgenerally has N pixels in a vertical direction and N pixels in ahorizontal direction, where N represents a nonnegative integer value.The pixels in a block may be arranged in rows and columns. Moreover,blocks need not necessarily have the same number of pixels in thehorizontal direction as in the vertical direction. For example, blocksmay comprise N×M pixels, where M is not necessarily equal to N.

Following intra-predictive or inter-predictive coding using the PUs of aCU, video encoder 20 may calculate residual data for the TUs of the CU.The PUs may comprise syntax data describing a method or mode ofgenerating predictive pixel data in the spatial domain (also referred toas the pixel domain) and the TUs may comprise coefficients in thetransform domain following application of a transform, e.g., a discretecosine transform (DCT), an integer transform, a wavelet transform, or aconceptually similar transform to residual video data. The residual datamay correspond to pixel differences between pixels of the unencodedpicture and prediction values corresponding to the PUs. Video encoder 20may form the TUs to include quantized transform coefficientsrepresentative of the residual data for the CU. That is, video encoder20 may calculate the residual data (in the form of a residual block),transform the residual block to produce a block of transformcoefficients, and then quantize the transform coefficients to formquantized transform coefficients. Video encoder 20 may form a TUincluding the quantized transform coefficients, as well as other syntaxinformation (e.g., splitting information for the TU).

As noted above, following any transforms to produce transformcoefficients, video encoder 20 may perform quantization of the transformcoefficients. Quantization generally refers to a process in whichtransform coefficients are quantized to possibly reduce the amount ofdata used to represent the coefficients, providing further compression.The quantization process may reduce the bit depth associated with someor all of the coefficients. For example, an n-bit value may be roundeddown to an m-bit value during quantization, where n is greater than m.

Following quantization, video encoder 20 may scan the transformcoefficients, producing a one-dimensional vector from thetwo-dimensional matrix including the quantized transform coefficients.The scan may be designed to place higher energy (and therefore lowerfrequency) coefficients at the front of the array and to place lowerenergy (and therefore higher frequency) coefficients at the back of thearray. In some examples, video encoder 20 may utilize a predefined scanorder to scan the quantized transform coefficients to produce aserialized vector that can be entropy encoded. In other examples, videoencoder 20 may perform an adaptive scan. After scanning the quantizedtransform coefficients to form a one-dimensional vector, video encoder20 may entropy encode the one-dimensional vector, e.g., according tocontext-adaptive variable length coding (CAVLC), context-adaptive binaryarithmetic coding (CABAC), syntax-based context-adaptive binaryarithmetic coding (SBAC), Probability Interval Partitioning Entropy(PIPE) coding or another entropy encoding methodology. Video encoder 20may also entropy encode syntax elements associated with the encodedvideo data for use by video decoder 30 in decoding the video data.

To perform CABAC, video encoder 20 may assign a context within a contextmodel to a symbol to be transmitted. The context may relate to, forexample, whether neighboring values of the symbol are non-zero or not.To perform CAVLC, video encoder 20 may select a variable length code fora symbol to be transmitted. Codewords in VLC may be constructed suchthat relatively shorter codes correspond to more probable symbols, whilelonger codes correspond to less probable symbols. In this way, the useof VLC may achieve a bit savings over, for example, using equal-lengthcodewords for each symbol to be transmitted. The probabilitydetermination may be based on a context assigned to the symbol.

In general, video decoder 30 performs a substantially similar, albeitreciprocal, process to that performed by video encoder 20 to decodeencoded data. For example, video decoder 30 inverse quantizes andinverse transforms coefficients of a received TU to reproduce a residualblock. Video decoder 30 uses a signaled prediction mode (intra- orinter-prediction) to form a predicted block. Then video decoder 30combines the predicted block and the residual block (on a pixel-by-pixelbasis) to reproduce the original block. Additional processing may beperformed, such as performing a deblocking process to reduce visualartifacts along block boundaries. Furthermore, video decoder 30 maydecode syntax elements using CABAC in a manner substantially similar to,albeit reciprocal to, the CABAC encoding process of video encoder 20.

In accordance with one example of the techniques of this disclosure, avideo coder (such as video encoder 20 or video decoder 30) may beconfigured to code video usability information (VUI) in a videoparameter set (VPS), including hypothetical reference decoder (HRD)parameters. Table 1 below describes an example VPS VUI byte sequencepayload (BSP) for HRD parameters in accordance with certain techniquesof this disclosure. In Table 1, italicized text indicates additionsrelative to the data structure described in the variant 2 attachment toJCTVC-R0010v2, while text identified using brackets and “removed:” (forexample, [removed: “example removed text”] represents removals from thedata structure described in the variant 2 attachment to JCTVC-R0010v2.

TABLE 1 vps_vui_bsp_hrd_params [removed: “parameters”]( ) { Descriptor vps_num_add_hrd_params [removed: “parameters”] ue(v)  for( i =vps_num_hrd_parameters; i < vps_num_hrd_parameters +  vps_num_add_hrd_params [removed: “parameters”]; i++ ) {   if( i > 0 ){    cprms_add_present_flag[ i ] u(1)    num_sub_layer_hrd_minus1[ i ]ue(v)   }   hrd_parameters( cprms_add_present_flag[ i ], num [removed:“vps_max”]_sub_hrd [removed: “layers”]_minus1[ i ] )  }  for( h = 1; h <NumOutputLayerSets; h++ )   for( i = 0; i < NumPartitioningSchemes[ h ];i++ ) {    bsp_hrd_params [removed: “parameters”]_present_flag[ h ][ i ]u(1)    if( bsp_hrd_params [removed: “parameters”]_present_flag[ h ][ i] ) {     for( t = 0; t <= MaxSubLayersInLayerSetMinus1[ OlsIdxToLsIdx[i ] ]; t++ ) {      num_bsp_schedules [removed: ue(v)“sched_combinations”]_minus1[ h ][ i ][ t ]      for( j = 0; j <=num_bsp_schedules [removed: “sched_combinations”]_minus1[ h ][ i ][ t ];j++ )       for( k = 0; k <= num_partitions_in_scheme_minus1[ h ][ i ];k++ ) {        bsp[removed: “_comb”]_hrd_idx[ h ][ i ][ t ][ j ][ k ]u(v)        bsp[removed: “_comb”]_sched_idx[ h ][ i ][ t ][ j ][ k ]ue(v)      }     }[removed: “}”]    }   } }

Example semantics for the syntax elements of Table 1 are describedbelow. Unchanged syntax elements that are not otherwise discussed belowmay retain the semantics as described in the variant 2 attachment toJCTVC-R0010v2. Again, italicized text represents additions, while[removed: “ ”] represents deletions.

vps_num_add_hrd_params [removed: “parameters”] specifies the number ofadditional hrd_parameters( ) syntax structures present in the VPS. Thevalue of vps_num_add_hrd_params [removed: “parameters”] shall be in therange of 0 to 1024—vps_num_hrd_parameters, inclusive.

cprms_add_present_flag[i] equal to 1 specifies that the HRD parametersthat are common for all sub-layers are present in the i-thhrd_parameters( ) syntax structure. cprms_add_present_flag[i] equal to 0specifies that the HRD parameters that are common for all sub-layers arenot present in the i-th hrd_parameters( ) syntax structure and arederived to be the same as the (i−1)-th hrd_parameters( ) syntaxstructure.

num_sub_layer_hrd_minus1[i] plus 1 specifies the number offixed_pic_rate_general_flag[ ] syntax elements in the i-thhrd_parameters( ) syntax structure. The value ofnum_sub_layer_hrd_minus1[i] shall be in the range of 0 tovps_max_sub_layers_minus1, inclusive.

bsp_hrd_params [removed: “parameters”]_present_flag[h][i] equal to 1specifies that the HRD parameters are present for all bitstreamparathions of the i-th partitioning schemes of the h-th OLS.bsp_hrd_params [removed: “parameters”]_present_flag[h][i] equal to 0specifies that the HRD parameters are not present for any bitstreampartitition of the i-th partitioning scheme of the h-th OLS.

num_bsp_schedules [removed: “sched_combinations”]_minus1[h][i][t] plus 1specifies the number of [removed: “combinations of”] delivery schedules[removed: “and hrd_parameters( )”] specified for bitstream partitions ofthe i-th partitioning scheme of the h-th OLS when HighestTid is equal tot. The value of num_bsp_schedules_minus1[h][i][t] shall be in the rangeof 0 to 31, inclusive.

The variable [removed: “SchedCombCnt”] BspSchedCnt [h][i][t] is setequal to num_bsp_schedules [removed:“sched_combinations”]_minus1[h][i][t]+1.

bsp [removed: “_comb”]_hrd_idx[h][i][t][j][k] specifies the index of thehrd_parameters( ) syntax structure in the VPS for the j-th [removed:“combination of a”] delivery schedule [removed: “and hrd_parameters( )”]specified for the k-th bitstream partition of the i-th partitioningscheme for the h-th OLS when HighestTid is equal to t. The length of thebsp [removed: “_comb”]_hrd_idx[h][i][t][j][k] syntax element is Ceil(Log2(vps_num_hrd_parameters+vps_num_add_hrd_params [removed:“parameters”])) bits. The value of bsp [removed:“_comb”]_hrd_idx[h][i][t][j][k] shall be in the range of 0 tovps_num_hrd_parameters+vps_num_add_hrd_params [removed: “parameters”]−1,inclusive.

bsp [removed: “_comb”]_sched_idx[h][i][t][j][k] specifies the index ofthe [removed: “a”] delivery schedule within thesub_layer_hrd_parameters(t) [removed: “hrd_parameters( )”] syntaxstructure of the hrd_parameters(t) syntax structure with the index bsp[removed: “_comb”]_hrd_idx[h][i][t][j][k], that is used [removed: “in”]as the j-th [removed: “combination of a”] delivery schedule [removed:“and hrd_parameters( )”] specified for the k-th bitstream partition ofthe i-th partitioning scheme for the h-th OLS when HighestTid is equalto t. The value of bsp [removed: “_comb”]_sched_idx[h][i][t][j][k] shallbe in the range of 0 to cpb_cnt_minus1[t[removed: “HighestTid”]],inclusive, where cpb_cnt_minus1[t[removed: “HighestTid”]] is found inthe sub_layer_hrd_parameters(t[removed: “HighestTid”]) syntax structurefrom the hrd_parameters( ) syntax structure corresponding to the indexbsp [removed: “_comb”]_hrd_idx[h][i][t][j][k].

In accordance with HEVC, other conventional HRD parameters may also besignaled in the HRD parameters syntax structure, although notnecessarily shown in Table 1 above. For example, the HRD parameters mayinclude fixed_pic_rate_within_cvs_flag[i], for which HEVC definessemantics as:

-   -   fixed_pic_rate_within_cvs_flag[i] equal to 1 indicates that,        when HighestTid is equal to i, the temporal distance between the        HRD output times of consecutive pictures in output order is        constrained as specified below.        fixed_pic_rate_within_cvs_flag[i] equal to 0 indicates that this        constraint may not apply.

The HRD parameters may also include anelemental_duration_in_tc_minus1[i] syntax element, for which HEVCdefines semantics as:

-   -   elemental_duration_in_tc_minus1 [i] plus 1 (when present)        specifies, when HighestTid is equal to i, the temporal distance,        in clock ticks, between the elemental units that specify the HRD        output times of consecutive pictures in output order as        specified below. The value of elemental_duration_in_tc_minus1[i]        shall be in the range of 0 to 2047, inclusive.

The HRD parameters may also include a low_delay_hrd_flag[i] syntaxelement, for which HEVC defines semantics as:

-   -   low_delay_hrd_flag[i] specifies the HRD operational mode, when        HighestTid is equal to i, as specified in Annex C. When not        present, the value of low_delay_hrd_flag[i] is inferred to be        equal to 0.

In the example of Table 1, num_sub_layer_hrd_minus1[i] represents anexample of a syntax element that indicates a number of sub-layers of abitstream for which hypothetical reference decoder (HRD) parameters arecoded. The number of sub-layers for which HRD parameters are coded maybe less than or equal to a maximum number of sub-layers indicated by avideo parameter set (VPS) of the bitstream. Thus, a video coder may codeHRD parameters for the number of sub-layers as indicated by the valuefor the syntax element and then process the bitstream using the HRDparameters. For example, video encoder 20 and video decoder 30 mayremove pictures from a decoded picture buffer according to the HRDparameters. Moreover, destination device 14 may display pictures removedfrom the decoded picture buffer using display device 32.

As also shown in the example of Table 1, a video coder may code a set ofHRD parameters for each sub-layer included in a multi-layer bitstream.In Table 1, the loop indicated by “for(t=0;t<=MaxSubLayersInLayerSetMinus1[OlsIdxToLsIdx[i]]; t++)” represents aloop over the number of sub-layers included in a particular layer set,which is performed for each of the available output layer sets. Withinthis loop, indexes for HRD parameters (bsp_hrd_idx) are signaled. Thus,this is one example technique for coding a number of HRD parameters thatis equal to the number of sub-layers of the bitstream. In particular,there is a one-to-one mapping between HRD parameters and the number ofsub-layers for each bitstream partition (that is, each output layerset).

Furthermore, a video coder (such as video encoder 20 or video decoder30) may be configured to code (encode or decode, respectively)information indicative of a bitstream partition initial arrival timeaccording to the example data structure of Table 2 below. Table 2represents an example of a bitstream partition initial arrival time SEImessage, which is changed relative to the variant 2 attachment ofJCTVC-R0010v2. Again, italicized text represents additions and [removed:“ ”] represents deletions.

TABLE 2 bsp_initial_arrival_time( payloadSize ) { Descriptor psIdx =sei_partitioning_scheme_idx if( NalHrdBpPresentFlag )  for( i = 0; i <[removed: “SchedCombCnt”] BspSchedCnt[ sei_ols_idx ][ psIdx [removed:“sei_partitioning_scheme_idx”] ][ maxTemporalId[ 0 ] ]; i++ )  nal_initial_arrival_delay[ i ] u(v) if( VclHrdBpPresentFlag )[removed: “else”]  for( i = 0; i < [removed: “SchedCombCnt”] BspSchedCnt[ sei_ols_idx ][ psIdx [removed: “sei_partitioning_scheme_idx”] ][maxTemporalId[ 0 ] ]; i++ )   vcl_initial_arrival_delay[ i ] u(v) }

Example semantics for the syntax elements of Table 2 are describedbelow. Unchanged syntax elements that are not otherwise discussed belowmay retain the semantics as described in the variant 2 attachment toJCTVC-R0010v2. Again, italicized text represents additions, while[removed: “ ”] represents deletions.

The bitstream partition initial arrival time SEI message specifies theinitial arrival times to be used in the bitstream-partition-specific CPBoperation.

When present, this SEI message shall be contained within a bitstreampartition nesting SEI message that is contained in a scalable nestingSEI message, and the same bitstream partition nesting SEI message shallalso contain a buffering period SEI message.

The following applies for bitstream partition nesting SEI message syntaxand semantics:

The syntax element initial_cpb_removal_delay_length_minus1 and thevariables NalHrdBpPresentFlag and VclHrdBpPresentFlag are found in orderived from syntax elements found in the hrd_parameters( ) syntaxstructure that is applicable to at least one of the operation points towhich the bitstream partition nesting SEI message applies.

[removed:

-   -   Let hrdParamIdx[i] for i in the range of 0 to        SchedCombCnt[sei_ols_idx][sei_partitioning_scheme_idx],        inclusive, be equal to the value of        bsp_comb_hrd_idx[olsIdx][partitioningSchemeIdx][i][bspIdx],        where olsIdx, partitioningSchemeIdx, and bspIdx are equal to        sei_ols_idx, sei_partitioning_scheme_idx, and bsp_idx,        respectively, of the bitstream partition nesting SEI message        containing this bitstream partition initial arrival time SEI        message. Let initialCpbRemovalDelayLength[i] be equal to        initial_cpb_removal_delay_length_minus1+1, where        initial_cpb_removal_delay_length_minus1 is found in the        hrdParamIdx[i]-th hrd_parameters( ) syntax structure in the        active VPS.]

nal_initial_arrival_delay[i] specifies the initial arrival time for thei-th delivery schedule [removed: “combination”] of the bitstreampartition to which this SEI message applies, when NAL HRD parameters arein use. The length, in bits, of the nal_initial_arrival_delay[i] syntaxelement is equal to initial_cpb_removal_delay_length_minus1+1 [removed:“initialCpbRemovalDelayLength[i]”].

vcl_initial_arrival_delay[i] specifies the initial arrival time for thei-th delivery schedule [removed: “combination”] of the bitstreampartition to which this SEI message applies, when VCL HRD parameters arein use. The length, in bits, of the vcl_initial_arrival_delay[i] syntaxelement is equal to initial_cpb_removal_delay_length_minus1+1 [removed:“initialCpbRemovalDelayLength[i]”].

Additional examples of these techniques are discussed below, e.g., withrespect to Tables 3 and 4. Table 3 represents an alternative to theexample of Table 1, while Table 4 represents an alternative to theexample of Table 4. Again, differences are shown relative to the variant2 attachment of JCTVC-R0010v2, where italicized text representsadditions and [removed: “ ”] represents deletions.

TABLE 3 vps_vui_bsp_hrd_params [removed: “parameters”] ( ) { Descriptor vps_num_add_hrd_params [removed: “parameters”] ue(v)  for( i =vps_num_hrd_parameters; i < vps_num_hrd_parameters +  vps_num_add_hrd_params [removed: “parameters”]; i++ ) {   if( i > 0 ){    cprms_add_present_flag[ i ] u(1)    num_sub_layer_hrd_minus1[ i ]ue(v)   }   hrd_parameters( cprms_add_present_flag[ i ], num [removed:“vps_max”]_sub_hrd [removed: “layers”]_minus1[ i ] )  }  for( h = 1; h <NumOutputLayerSets; h++ )   for( i = 0; i < NumPartitioningSchemes[ h ];i++ ) {    bsp_hrd_params [removed: “parameters”]_present_flag[ h ][ i ]u(1)    if( bsp_hrd_params [removed: “parameters”]_present_flag[ h ][ i] )[removed: “{“      [removed: “num_bsp_sched_combinations_minus1[ h ][i ]”] [removed: “ue(v)”]      [removed: “for( j = 0; j <=num_bsp_schedules_combinations_minus1[ h ][ i ][ t ]; j++ )”]       for(k = 0; k <= num_partitions_in_scheme_minus1[ h ][ i ]; k++ ) [removed:“{“]      bsp[removed: “_comb”]_hrd_idx[ h ][ i ][removed: “[ j ]”][ k ]u(v)        [removed: “bsp_comb_sched_idx[ h ][ i ][ j ][ k ]”][removed: “ue(v)”]      [removed: “}”]   } }

Example semantics for the syntax elements of Table 3 are describedbelow. Unchanged syntax elements that are not otherwise discussed belowmay retain the semantics as described in the variant 2 attachment toJCTVC-R0010v2. Again, italicized text represents additions, while[removed: “ ”] represents deletions.

vps_num_add_hrd_params [removed: “parameters”] specifies the number ofadditional hrd_parameters( ) syntax structures present in the VPS. Thevalue of vps_num_add_hrd_params [removed: “parameters”] shall be in therange of 0 to 1024—vps_num_hrd_parameters, inclusive.

cprms_add_present_flag[i] equal to 1 specifies that the HRD parametersthat are common for all sub-layers are present in the i-thhrd_parameters( ) syntax structure. cprms_add_present_flag[i] equal to 0specifies that the HRD parameters that are common for all sub-layers arenot present in the i-th hrd_parameters( ) syntax structure and arederived to be the same as the (i−1)-th hrd_parameters( ) syntaxstructure.

num_sub_layer_hrd_minus1[i] plus 1 specifies the number offixed_pic_rate_general_flag[ ] syntax elements in the i-thhrd_parameters( ) syntax structure. The value ofnum_sub_layer_hrd_minus1[i] shall be in the range of 0 tovps_max_sub_layers_minus1, inclusive.

bsp_hrd_params [removed: “parameters”]_present_flag[h][i] equal to 1specifies that the HRD parameters are present for all bitstreamparathions of the i-th partitioning schemes of the h-th OLS.bsp_hrd_params [removed: “parameters”]_present_flag[h][i] equal to 0specifies that the HRD parameters are not present for any bitstreampartitition of the i-th partitioning scheme of the h-th OLS.

[removed: “num_bsp_sched_combinations_minus1[h][i] plus 1 specifies thenumber of combinations of delivery schedules and hrd_parameters( )specified for bitstream partitions of the i-th partitioning scheme ofthe h-th OLS. [Ed. (MH): Add the allowed value range for this syntaxelement.]”]

[removed: “The variable SchedCombCnt[h][i] is set equal tonum_bsp_sched_combinations_minus1[h][i]+1.”]

bsp [removed: “_comb”]_hrd_idx[h][i][removed: “[j]”][k] specifies theindex of the hrd_parameters( ) syntax structure in the VPS for the[removed: “j-th combination of a delivery schedule and hrd_parameters( )specified for the”] k-th bitstream partition of the i-th partitioningscheme for the h-th OLS [removed: “ ”]. The length of the bsp [removed:“_comb”]_hrd_idx[h][i][removed: “[j]”][k] syntax element is Ceil(Log2(vps_num_hrd_parameters+vps_num_add_hrd_params [removed:“parameters”])) bits. The value of bsp [removed:“_comb”]_hrd_idx[h][i][removed: “[j]”][k] shall be in the range of 0 tovps_num_hrd_parameters+vps_num_add_hrd_params [removed: “parameters”]−1,inclusive.

[removed: “bsp_comb_sched_idx[h][i][j][k] specifies the index of adelivery schedule within the hrd_parameters( ) syntax structure with theindex bsp_comb_hrd_idx[h][i][j][k] that is used in the j-th combinationof a delivery schedule and hrd_parameters( ) specified for the k-thbitstream partition of the i-th partitioning scheme for the h-th OLS.The value of bsp_comb_sched_idx[h][i][j][k] shall be in the range of 0to cpb_cnt_minus1[HighestTid], inclusive, wherecpb_cnt_minus1[HighestTid] is found in thesub_layer_hrd_parameters(HighestTid) syntax structure from thehrd_parameters( ) syntax structure corresponding to the indexbsp_comb_hrd_idx[h][i][j][k]. [Ed. (YK): Both forms of“sub_layer_hrd_parameters(HighestTid)” and “sub_layer_hrd_parameters( )”are used in the document for referencing of the syntax structure. Checkwhether it would be better to consistently use just one of them.]”]

HEVC specifies the following semantics for thefixed_pic_rate_general_flag[i]: fixed_pic_rate_general_flag[i] equal to1 indicates that, when HighestTid is equal to i, the temporal distancebetween the HRD output times of consecutive pictures in output order isconstrained as specified below. fixed_pic_rate_general_flag[i] equal to0 indicates that this constraint may not apply.

In the example of Table 3, num_sub_layer_hrd_minus1[i] represents anexample of a syntax element that indicates a number of sub-layers of abitstream for which hypothetical reference decoder (HRD) parameters arecoded. The number of sub-layers for which HRD parameters are coded maybe less than or equal to a maximum number of sub-layers indicated by avideo parameter set (VPS) of the bitstream. Thus, a video coder may codeHRD parameters for the number of sub-layers as indicated by the valuefor the syntax element and then process the bitstream using the HRDparameters. For example, video encoder 20 and video decoder 30 mayremove pictures from a decoded picture buffer according to the HRDparameters. Moreover, destination device 14 may display pictures removedfrom the decoded picture buffer using display device 32.

Table 3 also represents another example technique by which a video codermay code a set of HRD parameters for each sub-layer included in amulti-layer bitstream. Contrasted with the techniques shown in Table 1,the example of Table 3 includes simply signaling an index to the list ofhrd_parameters( ) syntax structure for a set of sub-layers included in abitstream partition.

TABLE 4 bsp_initial_arrival_time( payloadSize ) { Descriptor if(NalHrdBpPresentFlag )  for( i = 0; i <= CpbCnt [removed: “SchedCombCnt[sei_ols_idx ][ sei_partitioning_scheme_idx ]”]; i++ )  nal_initial_arrival_delay[ i ] u(v) if( VclHrdBpPresentFlag )[removed: “else”]  for( i = 0; i <= CpbCnt [removed: “SchedCombCnt[sei_ols_idx ][ sei_partitioning_scheme_idx ]”]; i++ )  vcl_initial_arrival_delay[ i ] u(v) }

Example semantics for the syntax elements of Table 4 are describedbelow. Unchanged syntax elements that are not otherwise discussed belowmay retain the semantics as described in the variant 2 attachment toJCTVC-R0010v2. Again, italicized text represents additions, while[removed: “ ”] represents deletions.

The bitstream partition initial arrival time SEI message specifies theinitial arrival times to be used in the bitstream-partition-specific CPBoperation.

When present, this SEI message shall be contained within a bitstreampartition nesting SEI message that is contained in a scalable nestingSEI message, and the same bitstream partition nesting SEI message shallalso contain a buffering period SEI message.

The following applies for bitstream partition nesting SEI message syntaxand semantics:

The syntax element initial_cpb_removal_delay_length_minus1 and thevariables NalHrdBpPresentFlag and VclHrdBpPresentFlag are found in orderived from syntax elements found in the hrd_parameters( ) syntaxstructure that is applicable to at least one of the operation points towhich the bitstream partition nesting SEI message applies.

[removed:

-   -   Let hrdParamIdx[i] for i in the range of 0 to        SchedCombCnt[sei_ols_idx][sei_partitioning_scheme_idx],        inclusive, be equal to the value of        bsp_comb_hrd_idx[olsIdx][partitioningSchemeIdx][i][bspIdx],        where olsIdx, partitioningSchemeIdx, and bspIdx are equal to        sei_ols_idx, sei_partitioning_scheme_idx, and bsp_idx,        respectively, of the bitstream partition nesting SEI message        containing this bitstream partition initial arrival time SEI        message. Let initialCpbRemovalDelayLength[i] be equal to        initial_cpb_removal_delay_length_minus1+1, where        initial_cpb_removal_delay_length_minus1 is found in the        hrdParamIdx[i]-th hrd_parameters( ) syntax structure in the        active VPS.]

nal_initial_arrival_delay[i] specifies the initial arrival time for thei-th delivery schedule [removed: “combination”] of the bitstreampartition to which this SEI message applies, when NAL HRD parameters arein use. The length, in bits, of the nal_initial_arrival_delay[i] syntaxelement is equal to initial_cpb_removal_delay_length_minus1+1 [removed:“initialCpbRemovalDelayLength[i]”].

vcl_initial_arrival_delay[i] specifies the initial arrival time for thei-th delivery schedule [removed: “combination”] of the bitstreampartition to which this SEI message applies, when VCL HRD parameters arein use. The length, in bits, of the vcl_initial_arrival_delay[i] syntaxelement is equal to initial_cpb_removal_delay_length_minus1+1 [removed:“initialCpbRemovalDelayLength[i]”].

Video encoder 20 may further send syntax data, such as block-basedsyntax data, frame-based syntax data, and GOP-based syntax data, tovideo decoder 30, e.g., in a frame header, a block header, a sliceheader, or a GOP header. The GOP syntax data may describe a number offrames in the respective GOP, and the frame syntax data may indicate anencoding/prediction mode used to encode the corresponding frame.

Video encoder 20 and video decoder 30 each may be implemented as any ofa variety of suitable encoder or decoder circuitry, as applicable, suchas one or more microprocessors, digital signal processors (DSPs),application specific integrated circuits (ASICs), field programmablegate arrays (FPGAs), discrete logic circuitry, software, hardware,firmware or any combinations thereof. Each of video encoder 20 and videodecoder 30 may be included in one or more encoders or decoders, eitherof which may be integrated as part of a combined video encoder/decoder(CODEC). A device including video encoder 20 and/or video decoder 30 maycomprise an integrated circuit, a microprocessor, and/or a wirelesscommunication device, such as a cellular telephone.

FIG. 2 is a block diagram illustrating an example of video encoder 20that may implement techniques for improving hypothetical referencedecoder (HRD) parameter signaling. Video encoder 20 may perform intra-and inter-coding of video blocks within video slices. Intra-codingrelies on spatial prediction to reduce or remove spatial redundancy invideo within a given video frame or picture. Inter-coding relies ontemporal prediction to reduce or remove temporal redundancy in videowithin adjacent frames or pictures of a video sequence. Intra-mode (Imode) may refer to any of several spatial based coding modes.Inter-modes, such as uni-directional prediction (P mode) orbi-prediction (B mode), may refer to any of several temporal-basedcoding modes.

As shown in FIG. 2, video encoder 20 receives a current video blockwithin a video frame to be encoded. In the example of FIG. 2, videoencoder 20 includes mode select unit 40, reference picture memory 64(which may also be referred to as a decoded picture buffer (DPB)),summer 50, transform processing unit 52, quantization unit 54, andentropy encoding unit 56. Mode select unit 40, in turn, includes motioncompensation unit 44, motion estimation unit 42, intra-prediction unit46, and partition unit 48. For video block reconstruction, video encoder20 also includes inverse quantization unit 58, inverse transform unit60, and summer 62. A deblocking filter (not shown in FIG. 2) may also beincluded to filter block boundaries to remove blockiness artifacts fromreconstructed video. If desired, the deblocking filter would typicallyfilter the output of summer 62. Additional filters (in loop or postloop) may also be used in addition to the deblocking filter. Suchfilters are not shown for brevity, but if desired, may filter the outputof summer 50 (as an in-loop filter).

During the encoding process, video encoder 20 receives a video frame orslice to be coded. The frame or slice may be divided into multiple videoblocks. Motion estimation unit 42 and motion compensation unit 44perform inter-predictive encoding of the received video block relativeto one or more blocks in one or more reference frames to providetemporal prediction. Intra-prediction unit 46 may alternatively performintra-predictive encoding of the received video block relative to one ormore neighboring blocks in the same frame or slice as the block to becoded to provide spatial prediction. Video encoder 20 may performmultiple coding passes, e.g., to select an appropriate coding mode foreach block of video data.

Moreover, partition unit 48 may partition blocks of video data intosub-blocks, based on evaluation of previous partitioning schemes inprevious coding passes. For example, partition unit 48 may initiallypartition a frame or slice into LCUs, and partition each of the LCUsinto sub-CUs based on rate-distortion analysis (e.g., rate-distortionoptimization). Mode select unit 40 may further produce a quadtree datastructure indicative of partitioning of an LCU into sub-CUs. Leaf-nodeCUs of the quadtree may include one or more PUs and one or more TUs.

Mode select unit 40 may select one of the prediction modes, intra orinter, e.g., based on error results, and provides the resultingpredicted block to summer 50 to generate residual data and to summer 62to reconstruct the encoded block for use as a reference frame. Modeselect unit 40 also provides syntax elements, such as motion vectors,intra-mode indicators, partition information, and other such syntaxinformation, to entropy encoding unit 56.

Motion estimation unit 42 and motion compensation unit 44 may be highlyintegrated, but are illustrated separately for conceptual purposes.Motion estimation, performed by motion estimation unit 42, is theprocess of generating motion vectors, which estimate motion for videoblocks. A motion vector, for example, may indicate the displacement of aPU of a video block within a current video frame or picture relative toa predictive block within a reference frame (or other coded unit)relative to the current block being coded within the current frame (orother coded unit). A predictive block is a block that is found toclosely match the block to be coded, in terms of pixel difference, whichmay be determined by sum of absolute difference (SAD), sum of squaredifference (SSD), or other difference metrics. In some examples, videoencoder 20 may calculate values for sub-integer pixel positions ofreference pictures stored in reference picture memory 64. For example,video encoder 20 may interpolate values of one-quarter pixel positions,one-eighth pixel positions, or other fractional pixel positions of thereference picture. Therefore, motion estimation unit 42 may perform amotion search relative to the full pixel positions and fractional pixelpositions and output a motion vector with fractional pixel precision.

Motion estimation unit 42 calculates a motion vector for a PU of a videoblock in an inter-coded slice by comparing the position of the PU to theposition of a predictive block of a reference picture. The referencepicture may be selected from a first reference picture list (List 0) ora second reference picture list (List 1), each of which identify one ormore reference pictures stored in reference picture memory 64. Motionestimation unit 42 sends the calculated motion vector to entropyencoding unit 56 and motion compensation unit 44.

Motion compensation, performed by motion compensation unit 44, mayinvolve fetching or generating the predictive block based on the motionvector determined by motion estimation unit 42. Again, motion estimationunit 42 and motion compensation unit 44 may be functionally integrated,in some examples. Upon receiving the motion vector for the PU of thecurrent video block, motion compensation unit 44 may locate thepredictive block to which the motion vector points in one of thereference picture lists. Summer 50 forms a residual video block bysubtracting pixel values of the predictive block from the pixel valuesof the current video block being coded, forming pixel difference values,as discussed below. In general, motion estimation unit 42 performsmotion estimation relative to luma components, and motion compensationunit 44 uses motion vectors calculated based on the luma components forboth chroma components and luma components. Mode select unit 40 may alsogenerate syntax elements associated with the video blocks and the videoslice for use by video decoder 30 in decoding the video blocks of thevideo slice.

Intra-prediction unit 46 may intra-predict a current block, as analternative to the inter-prediction performed by motion estimation unit42 and motion compensation unit 44, as described above. In particular,intra-prediction unit 46 may determine an intra-prediction mode to useto encode a current block. In some examples, intra-prediction unit 46may encode a current block using various intra-prediction modes, e.g.,during separate encoding passes, and intra-prediction unit 46 (or modeselect unit 40, in some examples) may select an appropriateintra-prediction mode to use from the tested modes.

For example, intra-prediction unit 46 may calculate rate-distortionvalues using a rate-distortion analysis for the various testedintra-prediction modes, and select the intra-prediction mode having thebest rate-distortion characteristics among the tested modes.Rate-distortion analysis generally determines an amount of distortion(or error) between an encoded block and an original, unencoded blockthat was encoded to produce the encoded block, as well as a bitrate(that is, a number of bits) used to produce the encoded block.Intra-prediction unit 46 may calculate ratios from the distortions andrates for the various encoded blocks to determine which intra-predictionmode exhibits the best rate-distortion value for the block.

After selecting an intra-prediction mode for a block, intra-predictionunit 46 may provide information indicative of the selectedintra-prediction mode for the block to entropy encoding unit 56. Entropyencoding unit 56 may encode the information indicating the selectedintra-prediction mode. Video encoder 20 may include in the transmittedbitstream configuration data, which may include a plurality ofintra-prediction mode index tables and a plurality of modifiedintra-prediction mode index tables (also referred to as codeword mappingtables), definitions of encoding contexts for various blocks, andindications of a most probable intra-prediction mode, anintra-prediction mode index table, and a modified intra-prediction modeindex table to use for each of the contexts.

Video encoder 20 forms a residual video block by subtracting theprediction data from mode select unit 40 from the original video blockbeing coded. Summer 50 represents the component or components thatperform this subtraction operation. Transform processing unit 52 appliesa transform, such as a discrete cosine transform (DCT) or a conceptuallysimilar transform, to the residual block, producing a video blockcomprising transform coefficient values. Wavelet transforms, integertransforms, sub-band transforms, discrete sine transforms (DSTs), orother types of transforms could be used instead of a DCT. In any case,transform processing unit 52 applies the transform to the residualblock, producing a block of transform coefficients. The transform mayconvert the residual information from a pixel domain to a transformdomain, such as a frequency domain. Transform processing unit 52 maysend the resulting transform coefficients to quantization unit 54.Quantization unit 54 quantizes the transform coefficients to furtherreduce bit rate. The quantization process may reduce the bit depthassociated with some or all of the coefficients. The degree ofquantization may be modified by adjusting a quantization parameter.

Following quantization, entropy encoding unit 56 scans and entropyencodes the quantized transform coefficients. For example, entropyencoding unit 56 may perform context adaptive variable length coding(CAVLC), context adaptive binary arithmetic coding (CABAC), syntax-basedcontext-adaptive binary arithmetic coding (SBAC), probability intervalpartitioning entropy (PIPE) coding or another entropy coding technique.In the case of context-based entropy coding, context may be based onneighboring blocks. Following the entropy coding by entropy encodingunit 56, the encoded bitstream may be transmitted to another device(e.g., video decoder 30) or archived for later transmission orretrieval.

Inverse quantization unit 58 and inverse transform unit 60 apply inversequantization and inverse transformation, respectively, to reconstructthe residual block in the pixel domain. In particular, summer 62 addsthe reconstructed residual block to the motion compensated predictionblock earlier produced by motion compensation unit 44 orintra-prediction unit 46 to produce a reconstructed video block forstorage in reference picture memory 64. The reconstructed video blockmay be used by motion estimation unit 42 and motion compensation unit 44as a reference block to inter-code a block in a subsequent video frame.

Video encoder 20 generally uses the process discussed above to encodeeach block of each picture in a coded video sequence. In addition, insome examples, video encoder 20 may determine temporal layers to whichto assign each of the pictures. Furthermore, video encoder 20 may beconfigured to encode pictures of other layers, e.g., other views,scalable video coding layers, or the like. In any case, video encoder 20may further encode data indicating a layer to which each picturebelongs, for one or more layers (e.g., of various video dimensions).

In accordance with the techniques of this disclosure, video encoder 20may also encode other data structures, such as parameter sets including,for example, video parameter sets (VPSs), sequence parameter sets(SPSs), picture parameter sets (PPSs), supplemental enhancementinformation (SEI) messages, or the like. In accordance with thetechniques of this disclosure, video encoder 20 may encode a VPSincluding information described with respect to Tables 1 or 3 above,and/or an SEI message including information described with respect toTables 2 or 4 above.

For example, video encoder 20 may encode a value for a syntax elementthat indicates a number of sub-layers of a bitstream for whichhypothetical reference decoder (HRD) parameters (e.g., included in aVPS) are encoded. In accordance with the techniques of this disclosure,video encoder 20 may encode HRD parameters for each sub-layer of apartition of a bitstream, but avoid coding more HRD parameters thansub-layers of the partition. Thus, the number of HRD parameter datastructures for the partition may be less than the maximum number ofsub-layers, as indicated in the VPS. Furthermore, video encoder 20 mayprocess data of the bitstream using the HRD parameters. For example,video encoder 20 may discard decoded pictures from reference picturememory 64 according to data signaled in the HRD parameters.

As another example, which may be in addition to or in the alternative tothe examples discussed above, video encoder 20 may encode a syntaxelement representative of an initial arrival delay for video codinglayer HRD parameters if and only if a VclHrdBpPresentFlag is equal to 1(i.e., has a value of true). According to H.265, the value forVclHrdBpPresentFlag is set as follows:

-   -   If one or more of the following conditions are true, the value        of VclHrdBpPresentFlag is set equal to 1:        -   vcl_hrd_parameters_present_flag is present in the bitstream            and is equal to 1.        -   The need for presence of buffering periods for VCL HRD            operation to be present in the bitstream in buffering period            SEI messages is determined by the application, by some means            not specified in this Specification.    -   Otherwise, the value of VclHrdBpPresentFlag is set equal to 0.

Thus, in accordance with the techniques of this disclosure, videoencoder 20 may encode a syntax element representative of an initialarrival delay for video coding layer HRD parameters if and only if atleast one of video coding layer (VCL) HRD parameters are coded in thebitstream or when buffering period information for VCL HRD operationsare determined to be needed in the bitstream.

In this manner, video encoder 20 of FIG. 2 represents an example of avideo encoder configured to encode a value for a syntax element thatindicates a number of sub-layers of a bitstream for which hypotheticalreference decoder (HRD) parameters are coded, wherein the valueindicates that the number of sub-layers for which HRD parameters arecoded is less than a maximum number of sub-layers indicated by a videoparameter set (VPS) of the bitstream, encode HRD parameters for thenumber of sub-layers as indicated by the value for the syntax element,and process the bitstream using the HRD parameters.

Moreover, video encoder 20 represents an example of a video encoderconfigured to encode an initial arrival delay syntax element of abitstream partition initial arrival time supplemental enhancementinformation (SEI) message only when at least one of video coding layer(VCL) HRD parameters are coded in the bitstream or when buffering periodinformation for VCL HRD operations are determined to be needed in thebitstream. That is, video encoder 20 represents an example of a videoencoder configured to encode an initial arrival delay syntax element ofa bitstream partition initial arrival time supplemental enhancementinformation (SEI) message only when a VclHrdBpPresentFlag has a value oftrue.

FIG. 3 is a block diagram illustrating an example of video decoder 30that may implement techniques for improving hypothetical referencedecoder (HRD) parameter signaling. In the example of FIG. 3, videodecoder 30 includes an entropy decoding unit 70, motion compensationunit 72, intra prediction unit 74, inverse quantization unit 76, inversetransformation unit 78, reference picture memory 82 and summer 80. Videodecoder 30 may, in some examples, perform a decoding pass generallyreciprocal to the encoding pass described with respect to video encoder20 (FIG. 2). Motion compensation unit 72 may generate prediction databased on motion vectors received from entropy decoding unit 70, whileintra-prediction unit 74 may generate prediction data based onintra-prediction mode indicators received from entropy decoding unit 70.

During the decoding process, video decoder 30 receives an encoded videobitstream that represents video blocks of an encoded video slice andassociated syntax elements from video encoder 20. Entropy decoding unit70 of video decoder 30 entropy decodes the bitstream to generatequantized coefficients, motion vectors or intra-prediction modeindicators, and other syntax elements. Entropy decoding unit 70 forwardsthe motion vectors to and other syntax elements to motion compensationunit 72. Video decoder 30 may receive the syntax elements at the videoslice level and/or the video block level.

When the video slice is coded as an intra-coded (I) slice, intraprediction unit 74 may generate prediction data for a video block of thecurrent video slice based on a signaled intra prediction mode and datafrom previously decoded blocks of the current frame or picture. When thevideo frame is coded as an inter-coded (i.e., B, P or GPB) slice, motioncompensation unit 72 produces predictive blocks for a video block of thecurrent video slice based on the motion vectors and other syntaxelements received from entropy decoding unit 70. The predictive blocksmay be produced from one of the reference pictures within one of thereference picture lists. Video decoder 30 may construct the referenceframe lists, List 0 and List 1, using default construction techniquesbased on reference pictures stored in reference picture memory 82.Motion compensation unit 72 determines prediction information for avideo block of the current video slice by parsing the motion vectors andother syntax elements, and uses the prediction information to producethe predictive blocks for the current video block being decoded. Forexample, motion compensation unit 72 uses some of the received syntaxelements to determine a prediction mode (e.g., intra- orinter-prediction) used to code the video blocks of the video slice, aninter-prediction slice type (e.g., B slice, P slice, or GPB slice),construction information for one or more of the reference picture listsfor the slice, motion vectors for each inter-encoded video block of theslice, inter-prediction status for each inter-coded video block of theslice, and other information to decode the video blocks in the currentvideo slice.

Motion compensation unit 72 may also perform interpolation based oninterpolation filters. Motion compensation unit 72 may use interpolationfilters as used by video encoder 20 during encoding of the video blocksto calculate interpolated values for sub-integer pixels of referenceblocks. In this case, motion compensation unit 72 may determine theinterpolation filters used by video encoder 20 from the received syntaxelements and use the interpolation filters to produce predictive blocks.

Inverse quantization unit 76 inverse quantizes, i.e., de-quantizes, thequantized transform coefficients provided in the bitstream and decodedby entropy decoding unit 70. The inverse quantization process mayinclude use of a quantization parameter QP_(Y) calculated by videodecoder 30 for each video block in the video slice to determine a degreeof quantization and, likewise, a degree of inverse quantization thatshould be applied.

Inverse transform unit 78 applies an inverse transform, e.g., an inverseDCT, an inverse integer transform, or a conceptually similar inversetransform process, to the transform coefficients in order to produceresidual blocks in the pixel domain.

After motion compensation unit 72 generates the predictive block for thecurrent video block based on the motion vectors and other syntaxelements, video decoder 30 forms a decoded video block by summing theresidual blocks from inverse transform unit 78 with the correspondingpredictive blocks generated by motion compensation unit 72. Summer 80represents the component or components that perform this summationoperation. If desired, a deblocking filter may also be applied to filterthe decoded blocks in order to remove blockiness artifacts. Other loopfilters (either in the coding loop or after the coding loop) may also beused to smooth pixel transitions, or otherwise improve the videoquality. The decoded video blocks in a given frame or picture are thenstored in reference picture memory 82, which stores reference picturesused for subsequent motion compensation. Reference picture memory 82also stores decoded video for later presentation on a display device,such as display device 32 of FIG. 1.

Video decoder 30 generally uses the process discussed above to decodeeach block of each picture in a coded video sequence. In addition, insome examples, video decoder 30 may decode data indicating temporallayers to which pictures are assigned. Furthermore, video decoder 30 maybe configured to decode pictures of other layers, e.g., other views,scalable video coding layers, or the like. In any case, video decoder 30may further decode data indicating a layer to which each picturebelongs, for one or more layers (e.g., of various video dimensions).

In accordance with the techniques of this disclosure, video decoder 30may also decode other data structures, such as parameter sets including,for example, video parameter sets (VPSs), sequence parameter sets(SPSs), picture parameter sets (PPSs), supplemental enhancementinformation (SEI) messages, or the like. In accordance with thetechniques of this disclosure, video decoder 30 may decode a VPSincluding information described with respect to Tables 1 or 3 above,and/or an SEI message including information described with respect toTables 2 or 4 above.

For example, video decoder 30 may decode a value for a syntax elementthat indicates a number of sub-layers of a bitstream for whichhypothetical reference decoder (HRD) parameters (e.g., included in aVPS) are decoded. In accordance with the techniques of this disclosure,video decoder 30 may decode HRD parameters for each sub-layer of apartition of a bitstream, but avoid coding more HRD parameters thansub-layers of the partition. Thus, the number of HRD parameter datastructures for the partition may be less than the maximum number ofsub-layers, as indicated in the VPS. Furthermore, video decoder 30 mayprocess data of the bitstream using the HRD parameters. For example,video decoder 30 may output and/or discard decoded pictures fromreference picture memory 82 according to data signaled in the HRDparameters. In particular, video decoder 30 may output decoded picturesto a video display, such as display device 32, to cause the videodisplay to present the decoded pictures.

As another example, which may be in addition to or in the alternative tothe examples discussed above, video decoder 30 may decode a syntaxelement representative of an initial arrival delay for video codinglayer HRD parameters if and only if a VclHrdBpPresentFlag is equal to 1(i.e., has a value of true). According to H.265, the value forVclHrdBpPresentFlag is set as follows:

-   -   If one or more of the following conditions are true, the value        of VclHrdBpPresentFlag is set equal to 1:        -   vcl_hrd_parameters_present_flag is present in the bitstream            and is equal to 1.        -   The need for presence of buffering periods for VCL HRD            operation to be present in the bitstream in buffering period            SEI messages is determined by the application, by some means            not specified in this Specification.    -   Otherwise, the value of VclHrdBpPresentFlag is set equal to 0.

Thus, in accordance with the techniques of this disclosure, videodecoder 30 may decode a syntax element representative of an initialarrival delay for video coding layer HRD parameters if and only if atleast one of video coding layer (VCL) HRD parameters are coded in thebitstream or when buffering period information for VCL HRD operationsare determined to be needed in the bitstream.

In this manner, video decoder 30 of FIG. 3 represents an example of avideo decoder configured to decode a value for a syntax element thatindicates a number of sub-layers of a bitstream for which hypotheticalreference decoder (HRD) parameters are coded, wherein the valueindicates that the number of sub-layers for which HRD parameters arecoded is less than a maximum number of sub-layers indicated by a videoparameter set (VPS) of the bitstream, decode HRD parameters for thenumber of sub-layers as indicated by the value for the syntax element,and process the bitstream using the HRD parameters.

Moreover, video decoder 30 represents an example of a video decoderconfigured to decode an initial arrival delay syntax element of abitstream partition initial arrival time supplemental enhancementinformation (SEI) message only when at least one of video coding layer(VCL) HRD parameters are coded in the bitstream or when buffering periodinformation for VCL HRD operations are determined to be needed in thebitstream. That is, video decoder 30 represents an example of a videodecoder configured to decode an initial arrival delay syntax element ofa bitstream partition initial arrival time supplemental enhancementinformation (SEI) message only when a VclHrdBpPresentFlag has a value oftrue. Video decoder 30 may determine whether bits of the bitstreamcorrespond to the bitstream partition initial arrival time SEI message,or a different data structure, based on these techniques, and therebycorrectly parse the bitstream.

FIG. 4 is a flowchart illustrating an example method for encoding videodata according to the techniques of this disclosure. Although describedwith respect to video encoder 20 (FIGS. 1 and 2), it should beunderstood that other devices may be configured to perform a methodsimilar to that of FIG. 4.

In this example, video encoder 20 initially determines a maximum numberof sub-layers of a bitstream (150). Video encoder 20 also signals themaximum number of sub-layers in a video parameter set (VPS) (152) forthe bitstream. The bitstream is ultimately partitioned into variouspartitions, each of which includes a particular subset of thesub-layers. Thus, certain partitions will include fewer than the maximumnumber of sub-layers.

Video encoder 20 may then determine sub-layers in a bitstream partition(154). Video encoder 20 may then signal HRD parameters for eachsub-layer in the partition (156). For instance, as shown in Tables 1 and3, video encoder 20 may encode values for bsp_hrd_idx syntax elements.In particular, in Table 1, video encoder 20 may encode values forbsp_hrd_idx[h][i][t][j][k], while in Table 3, video encoder 20 mayencode values for bsp_hrd_idx[h][i][j][k]. In Table 1, these valuesoccur within nested loops over the number of output layer sets,partitioning schemes, and sub-layers in the layer set, whereas in Table3, these values occur within nested loops over the number of outputlayer sets and partitioning schemes.

Video encoder 20 also encodes pictures of the sub-layers (158), decodesthe encoded pictures of the sub-layers (160), and stores the decodedpictures in a decoded picture buffer (DPB) (162), such as referencepicture memory 64 (FIG. 2). Video encoder 20 stores decoded versions ofthe encoded pictures for subsequent use as reference pictures, such thatsubsequent prediction from these versions of the reference pictures willbe the same as versions ultimate decoded by a decoder, such as videodecoder 30. Furthermore, video encoder 20 removes decoded pictures fromthe DPB according to the HRD parameters (164).

Moreover, in accordance with certain techniques of this disclosure,video encoder 20 may conditionally encode data of a bitstream partitioninitial arrival time SEI message (166). In particular, video encoder 20may encode an initial arrival delay syntax element of the bitstreampartition initial arrival time SEI message only after determining that aVclHrdBpPresentFlag has a value of true (i.e., 1), e.g., if and only ifat least one of video coding layer (VCL) HRD parameters are coded in thebitstream or when buffering period information for VCL HRD operationsare determined to be needed in the bitstream.

In this manner, the method of FIG. 4 represents an example of a methodincluding coding (encoding, in this example) a value for a syntaxelement that indicates a number of sub-layers of a bitstream for whichhypothetical reference decoder (HRD) parameters are coded, wherein thevalue indicates that the number of sub-layers for which HRD parametersare coded is less than a maximum number of sub-layers indicated by avideo parameter set (VPS) of the bitstream, coding (encoding, in thisexample) HRD parameters for the number of sub-layers as indicated by thevalue for the syntax element, and processing the bitstream using the HRDparameters.

FIG. 5 is a flowchart illustrating an example method for decoding videodata according to the techniques of this disclosure. Although describedwith respect to video decoder 30 (FIGS. 1 and 3), it should beunderstood that other devices may be configured to perform a methodsimilar to that of FIG. 5.

In this example, video decoder 30 initially decodes a video parameterset (VPS) indicating a maximum number of sub-layers of a bitstream(200). The bitstream is ultimately partitioned into various partitions,each of which includes a particular subset of the sub-layers. Thus,certain partitions include fewer than the maximum number of sub-layers.

Video decoder 30 may then determine sub-layers in a bitstream partition(202). Video decoder 30 may then decode HRD parameters for eachsub-layer in the partition (204). For instance, as shown in Tables 1 and3, video decoder 30 may decode values for bsp_hrd_idx syntax elements.In particular, in Table 1, video decoder 30 may decode values forbsp_hrd_idx[h][i][t][j][k], while in Table 3, video decoder 30 maydecode values for bsp_hrd_idx[h][i][j][k]. In Table 1, these valuesoccur within nested loops over the number of output layer sets,partitioning schemes, and sub-layers in the layer set, whereas in Table3, these values occur within nested loops over the number of outputlayer sets and partitioning schemes.

Video decoder 30 also decodes encoded pictures of the sub-layers (206)and stores the decoded pictures in a decoded picture buffer (DPB) (208),such as reference picture memory 82 (FIG. 3). Video decoder 30 storesthe decoded pictures for subsequent use as reference pictures, such thatsubsequent prediction from these versions of the reference pictures isthe same as versions ultimate decoded by a decoder, such as videodecoder 30. Moreover, video decoder 30 stores the decoded pictures suchthat video decoder 30 can output the decoded pictures an appropriatetime. Thus, video decoder 30 removes and outputs decoded pictures fromthe DPB according to the HRD parameters (210).

Moreover, in accordance with certain techniques of this disclosure,video decoder 30 may conditionally decode data of a bitstream partitioninitial arrival time SEI message (212). In particular, video decoder 30may decode an initial arrival delay syntax element of the bitstreampartition initial arrival time SEI message only after determining that aVclHrdBpPresentFlag has a value of true (i.e., 1), e.g., if and only ifat least one of video coding layer (VCL) HRD parameters are coded in thebitstream or when buffering period information for VCL HRD operationsare determined to be needed in the bitstream. That is, a parser (notshown) associated with video decoder 30 may interpret certain bits ofthe bitstream as either belonging to the syntax element of the bitstreampartition initial arrival time SEI message, or a separate syntaxelement. In other words, the parser may differentiate between bits ofthe bitstream that correspond to the HRD parameters and bits of thebitstream that correspond to syntax elements following the HRDparameters.

In this manner, the method of FIG. 5 represents an example of a methodincluding coding (decoding, in this example) a value for a syntaxelement that indicates a number of sub-layers of a bitstream for whichhypothetical reference decoder (HRD) parameters are coded, wherein thevalue indicates that the number of sub-layers for which HRD parametersare coded is less than a maximum number of sub-layers indicated by avideo parameter set (VPS) of the bitstream, coding (decoding, in thisexample) HRD parameters for the number of sub-layers as indicated by thevalue for the syntax element, and processing the bitstream using the HRDparameters.

It is to be recognized that depending on the example, certain acts orevents of any of the techniques described herein can be performed in adifferent sequence, may be added, merged, or left out altogether (e.g.,not all described acts or events are necessary for the practice of thetechniques). Moreover, in certain examples, acts or events may beperformed concurrently, e.g., through multi-threaded processing,interrupt processing, or multiple processors, rather than sequentially.

In one or more examples, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored on or transmitted over as oneor more instructions or code on a computer-readable medium and executedby a hardware-based processing unit. Computer-readable media may includecomputer-readable storage media, which corresponds to a tangible mediumsuch as data storage media, or communication media including any mediumthat facilitates transfer of a computer program from one place toanother, e.g., according to a communication protocol. In this manner,computer-readable media generally may correspond to (1) tangiblecomputer-readable storage media which is non-transitory or (2) acommunication medium such as a signal or carrier wave. Data storagemedia may be any available media that can be accessed by one or morecomputers or one or more processors to retrieve instructions, codeand/or data structures for implementation of the techniques described inthis disclosure. A computer program product may include acomputer-readable medium.

By way of example, and not limitation, such computer-readable storagemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage, or other magnetic storage devices, flashmemory, or any other medium that can be used to store desired programcode in the form of instructions or data structures and that can beaccessed by a computer. Also, any connection is properly termed acomputer-readable medium. For example, if instructions are transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared, radio, and microwave, then thecoaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. It should be understood, however, thatcomputer-readable storage media and data storage media do not includeconnections, carrier waves, signals, or other transitory media, but areinstead directed to non-transitory, tangible storage media. Disk anddisc, as used herein, includes compact disc (CD), laser disc, opticaldisc, digital versatile disc (DVD), floppy disk and Blu-ray disc, wheredisks usually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above should also be includedwithin the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablegate arrays (FPGAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the term “processor,” as used herein may referto any of the foregoing structure or any other structure suitable forimplementation of the techniques described herein. In addition, in someaspects, the functionality described herein may be provided withindedicated hardware and/or software modules configured for encoding anddecoding, or incorporated in a combined codec. Also, the techniquescould be fully implemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinteroperative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.

Various examples have been described. These and other examples arewithin the scope of the following claims.

What is claimed is:
 1. A method of coding video data, the methodcomprising: coding, by a processor, a value for a syntax element thatindicates a number of sub-layers of a bitstream for which hypotheticalreference decoder (HRD) parameters are coded, wherein the valueindicates that the number of sub-layers for which the BIRD parametersare coded is less than a maximum number of sub-layers indicated by avideo parameter set (VPS) of the bitstream; coding, by the processor,the HRD parameters for the number of sub-layers as indicated by thevalue for the syntax element; and processing, by the processor, thebitstream using the HRD parameters, wherein processing the bitstreamcomprises coding one or more pictures of the sub-layers of the bitstreamusing the HRD parameters.
 2. The method of claim 1, wherein thebitstream comprises a plurality of HRD_parameters( ) syntax structures,and wherein coding the value for the syntax element comprises coding avalue for a num_sub_layer_hrd_minus1[i] syntax element for an ithHRD_parameter( ) syntax structure of the plurality of HRD_parameter( )syntax structures, wherein i is an integer value.
 3. The method of claim1, wherein the sub-layers comprise temporal sub-layers, and whereincoding the HRD parameters comprises coding a number, equal to the numberof temporal sub-layers for which the HRD parameters are coded, of syntaxelements indicative of at least whether temporal distances between BIRDoutput times of consecutive pictures in output order are constrained fora temporal sub-layer of the bitstream.
 4. The method of claim 3, whereinthe syntax elements indicative of at least whether the temporaldistances between BIRD output times of consecutive pictures in outputorder are constrained comprise at least one offixed_pic_rate_general_flag[ ] syntax elements orfixed_pic_rate_within_CVS_flag[ ] syntax elements.
 5. The method ofclaim 1, wherein coding the HRD parameters comprises coding one or moresyntax elements indicative of one or more of a temporal distance, inclock ticks, between elemental units that specify BIRD output times ofconsecutive pictures for a corresponding one of the sub-layers or an HRDoperational mode of the corresponding one of the sub-layers.
 6. Themethod of claim 5, wherein the syntax elements indicative of a temporaldistance, in clock ticks, between elemental units that specify BIRDoutput times of consecutive pictures compriseelemental_duration_in_tc_minus1[ ] syntax elements, and wherein thesyntax elements indicative of an HRD operational mode compriselow_delay_hrd_flag[ ] syntax elements.
 7. The method of claim 1, whereincoding the one or more pictures comprises: decoding encoded pictures ofthe bitstream; storing the decoded pictures in a decoded picture buffer(DPB); and removing the decoded pictures from the DPB according to theHRD parameters.
 8. The method of claim 7, further comprising encodingpictures to form the encoded pictures of the bitstream prior to decodingthe encoded pictures.
 9. The method of claim 1, further comprisingcoding, by the processor, an initial arrival delay syntax element of abitstream partition initial arrival time supplemental enhancementinformation (SEI) message only when at least one of video coding layer(VCL) HRD parameters are coded in the bitstream or when buffering periodinformation for VCL HRD operations are determined to be needed in thebitstream.
 10. The method of claim 1, further comprising coding, by theprocessor, an initial arrival delay syntax element of a bitstreampartition initial arrival time supplemental enhancement information(SET) message only in response to determining that a VclHrdBpPresentFlagfor the bitstream has a value of true.
 11. The method of claim 1, themethod being executable on a wireless communication device, wherein thedevice comprises: a memory configured to store the syntax element andthe HRD parameters; the processor, the processor being configured toexecute instructions to process the syntax element and the HRDparameters stored in the memory; and a receiver for receiving a signalincluding the syntax element and the HRD parameters and for storing thesyntax element and the HRD parameters to the memory.
 12. The method ofclaim 11, wherein the wireless communication device is a cellulartelephone and the signal is received by the receiver and modulatedaccording to a cellular communication standard.
 13. A device for codingvideo data, the device comprising: a memory configured to store videodata; and a video coder comprising one or more processors implementedusing circuitry, the one or more processors being configured to: code avalue for a syntax element of the video data that indicates a number ofsub-layers of a bitstream for which hypothetical reference decoder (HRD)parameters are coded, wherein the value indicates that the number ofsub-layers for which the HRD parameters are coded is less than a maximumnumber of sub-layers indicated by a video parameter set (VPS) of thebitstream; code the HRD parameters for the number of sub-layers asindicated by the value for the syntax element; and process the bitstreamusing the HRD parameters, wherein to process the bitstream, the one ormore processors are configured to code one or more pictures of thesub-layers of the bitstream using the HRD parameters.
 14. The device ofclaim 13, wherein the sub-layers comprise temporal sub-layers, andwherein the one or more processors are configured to code a number,equal to the number of temporal sub-layers for which the HRD parametersare coded, of syntax elements indicative of at least whether temporaldistances between HRD output times of consecutive pictures in outputorder are constrained corresponding to a temporal sub-layer of thebitstream.
 15. The device of claim 13, wherein to code the HRDparameters, the one or more processors are configured to code one ormore syntax elements indicative of one or more of a temporal distance,in clock ticks, between elemental units that specify HRD output times ofconsecutive pictures for a corresponding one of the sub-layers or an HRDoperational mode of the corresponding one of the sub-layers.
 16. Thedevice of claim 13, wherein the video coder comprises a video encoder.17. The device of claim 13, wherein the one or more processors areconfigured to code an initial arrival delay syntax element of abitstream partition initial arrival time supplemental enhancementinformation (SEI) message only when at least one of video coding layer(VCL) HRD parameters are coded in the bitstream or when buffering periodinformation for VCL HRD operations are determined to be needed in thebitstream.
 18. The device of claim 13, wherein the one or moreprocessors are configured to code an initial arrival delay syntaxelement of a bitstream partition initial arrival time supplementalenhancement information (SEI) message only in response to determiningthat a VclHrdBpPresentFlag for the bitstream has a value of true. 19.The device of claim 13, further comprising at least one of a camera tocapture the one or more pictures of the sub-layers or a display todisplay the one or more pictures of the sub-layers.
 20. The device ofclaim 13, wherein the device comprises at least one of: an integratedcircuit; a microprocessor; or a wireless communication device.
 21. Thedevice of claim 13, wherein the device is a wireless communicationdevice, and wherein the video coder comprises a video decoder, thedevice further comprising a receiver configured to receive a signalincluding the syntax element and the HRD parameters and to store thesyntax element and the HRD parameters to the memory.
 22. The device ofclaim 21, wherein the wireless communication device is a cellulartelephone and the signal is received by the transceiver and modulatedaccording to a cellular communication standard.
 23. A device for codingvideo data, the device comprising: means for coding a value for a syntaxelement that indicates a number of sub-layers of a bitstream for whichhypothetical reference decoder (HRD) parameters are coded, wherein thevalue indicates that the number of sub-layers for which the BIRDparameters are coded is less than a maximum number of sub-layersindicated by a video parameter set (VPS) of the bitstream; means forcoding the HRD parameters for the number of sub-layers as indicated bythe value for the syntax element; and means for processing the bitstreamusing the HRD parameters, wherein the means for processing the bitstreamcomprises means for coding one or more pictures of the sub-layers of thebitstream using the HRD parameters.
 24. The device of claim 23, whereinthe sub-layers comprise temporal sub-layers, wherein the means forcoding the HRD parameters comprises means for coding a number, equal tothe number of temporal sub-layers for which the HRD parameters arecoded, of syntax elements indicative of at least whether temporaldistances between BIRD output times of consecutive pictures in outputorder are constrained for a temporal sub-layer of the bitstream.
 25. Thedevice of claim 23, wherein the means for coding the HRD parameterscomprise means for coding one or more syntax elements indicative of oneor more of a temporal distance, in clock ticks, between elemental unitsthat specify BIRD output times of consecutive pictures for acorresponding one of the sub-layers or an HRD operational mode of thecorresponding one of the sub-layers.
 26. The device of claim 23, whereinthe means for coding the HRD parameters comprises means for decoding theHRD parameters, and wherein the means for decoding the HRD parameterscomprises means for configuring a parser to differentiate between bitsof the bitstream that correspond to the BIRD parameters and bits of thebitstream that correspond to syntax elements following the HRDparameters.
 27. The device of claim 23, further comprising means forcoding an initial arrival delay syntax element of a bitstream partitioninitial arrival time supplemental enhancement information (SEI) messageonly when at least one of video coding layer (VCL) HRD parameters arecoded in the bitstream or when buffering period information for VCL HRDoperations are determined to be needed in the bitstream.
 28. The deviceof claim 23, further comprising means for coding an initial arrivaldelay syntax element of a bitstream partition initial arrival timesupplemental enhancement information (SEI) message only in response todetermining that a VclHrdBpPresentFlag for the bitstream has a value oftrue.
 29. A non-transitory computer-readable storage medium havingstored thereon instructions that, when executed, cause a processor of adevice for coding video data to: code a value for a syntax element thatindicates a number of sub-layers of a bitstream for which hypotheticalreference decoder (HRD) parameters are coded, wherein the valueindicates that the number of sub-layers for which the HRD parameters arecoded is less than a maximum number of sub-layers indicated by a videoparameter set (VPS) of the bitstream; code the HRD parameters for thenumber of sub-layers as indicated by the value for the syntax element;and process the bitstream using the HRD parameters, wherein theinstructions that cause the processor to process the bitstream compriseinstructions that cause the processor to code one or more pictures ofthe sub-layers of the bitstream using the BIRD parameters.
 30. Thenon-transitory computer-readable storage medium of claim 29, wherein thesub-layers comprise temporal sub-layers, and wherein the instructionsthat cause the processor to code the BIRD parameters comprisesinstructions that cause the processor to code a number, equal to thenumber of temporal sub-layers for which the HRD parameters are coded, ofsyntax elements indicative of at least whether temporal distancesbetween HRD output times of consecutive pictures in output order areconstrained for a temporal sub-layer of the bitstream.